Laser light is a light source emitting monochromatic coherent beams, with high luminance and strong directionality. Owing to the numerous advantages, the laser light has been gradually applied as a light source in the technical field of projection display in recent years. However, because of the high coherence of laser, the speckle effect is inevitable, such phenomenon is especially obvious in the solutions within which a pure laser light is used as the light source, and it also exists in the solutions within which a laser light and a fluorescent light are used, as well as in the solutions within which the mixed light source of a laser light and a LED is used. The speckle refers to the spatial interference of the light after scattering when a coherent light source irradiates on a rough object, and the spatial interference of the light is owing to the same wave length and the constant phase of the light. There will be some constructive spatial interference and some destructive spatial interference, the final result is that alternated light and shade granular spots will appear on the screen, namely, some unfocused spots will flash, it is easy to feel dizzy after watching for long time. And it will undoubtedly result in the quality reduction of projected images to lower the user's experience of watching.
The use of a bicolor laser light source improves the overall luminance of the laser light source to satisfy the need of the luminance in the field of laser projection. However, the speckle problems caused by the laser light itself also will be aggravated, which becomes an obstacle to the popularization and application of the bicolor laser light.
How to reduce the speckle effect of a laser light caused by its inherent qualities at the same time of applying a bicolor laser light source has become a technical problem to be solved.